Internal-combustion-operated air-compressors



March 20, 1956 B. c. LOVATT 2,739,021

INTERNAL-COMBUSTION-OPERATED AIR-COMPRESSORS Filed Feb. 11, 1955 INTERNAL-COMBUSTION-OPERATED AIR-COMPRESSORS Bernard Charles Lovatt, Sunbury-oh-Thames, England,

assignor to Alan Muntz & CompanyLimited, Hounslow, England, a British company Application February 11,,1953, Serial No. 336,383 I Claims priority, application Great Britain December 10, 1951 6 Claims. 01. 309-17 The present invention relates to internaLcombustionoperated air-compressors of the free-piston type having a pair of opposed free pistons arranged to operate in a common internal-combustion cylinder on a two-stroke compression ignition cycle and rigidly connected by two piston rods respectively to two further pistons, at least one of which further pistons is a compressor piston operating in a compressor cylinder and serving for scavenging the internal combustion cylinder as well as for delivering air under pressure, while the other of said further pistons may be a cushion piston operating in a pneumatic cushion cylinder. The above-mentioned pairof opposed free pistons will be referred to for convenience as diesel pistons.

Each piston rod, in known engines of this kind, consists of a tubular trunk, one end of which forms a spigot on which the diesel piston is rigidly fixed by being shrunk on. Thisarrangement, however, has a number of disadvantages, the chief of which is that the removal of the diesel piston from the piston rod for servicing or replacement'is a slow and diificult operation.

The present invention accordingly has for its object to make the diesel piston removable from its piston rod without interfering with its cooling and, with this end in view, aims at the provision of a detachable connection which will not obstruct the passage of the oilsplash between the engine case and the inside of the skirt of the diesel piston.

According to the present invention, a substantial clearance is provided between the piston rod and the skirt of the diesel piston, which clearance extends from the lower edge of the skirt towards the crown of the piston over a substantial distance, e. g. over a distance greater than half the total length of the piston, whilst the extreme end portion of the piston rod is a close coaxial fit within the diesel piston beyond this clearance and is held up against the crown of the diesel piston by a pair of screwthreaded tension studs interconnecting the open end of the piston skirt with a pair of diametrically opposite radial projections carried by the piston rod and located adjacent the mouth of the said clearance. These radial projections are preferably designed so as to obstruct as little as possible the annular space at the mouth of the said clearance, and in any case they should not obstruct more than about one quarter of said annular space. Consequently the lubricating oil from the engine bearings, splashing to-and-fro in the engine case, will circulate in the form of a mist or in small droplets into and out of the above-mentioned clearance. Thus, as it sweeps over the interior surface of the piston skirt and the opposite surface of the piston rod, it will carry away from these surfaces the heat transmitted to them through a relatively short distance from the crown of the piston where the spigot and socket connection ensures good thermal contact between the piston and the piston rod.

The invention will now be described in greater detail by way of example with reference to the accompanying drawings, in which:

ice

Fig. 1 illustrates in plan one of the two piston assemblies of a two-stroke, compression-ignition free-piston compressor,

Fig.2 llustrates a diesellpiston forming part of this assembly in cross-section on an'enlarged scale and shows details of the m'eansby'fwhichlthis piston'is secured to one end of the piston rod of the assembly, v I

Fig. 3 is a section on the line III-:IIIin Fig. 2, and

Fig. 4 is a section on the line IV IV in Fig; 3.

The assembly illustrated in Fig. 1 comprises a 4 /2 inch diameter diesel piston lficonnected by a tubular piston rod 2 to a 10% inch diameter piston 3 which, in

the case of this piston assembly, is the compressorpiston,

though the corresponding piston of the other piston assembly of the engine serves as aicushion' piston. The'piston rod 2 also'carries intermediate the two pistons 1' and '3 a cross-head 4.which is coupled by connecting links 5, 6 to a synchronizing linkage (not shown) which is similarly coupled to a cross-head on the other piston assembly of the engine.

The external diameter of the piston rod 2, for the greater part of its length from the compressor piston 3 up to and including the part on which the cross-head 4 is mounted, is about 2 inches. Thereafter this external diameter is increased to about 2% inches in such a manner as to form anannularshoulder 7 which provides support for the. cross-head .in a direction parallel to'the axis of the pistonrod 2; The 2 /2 inch diameter portion of thepiston rod 2 extends for about 5 inches towards the crown of the dieselpiston. 1 before being enlarged so as to merge into a 2% inch diameter cylindrical locating portion 8 (Fig. 2) which is approximately 2 inches long and the extreme end of which'bears'against an annular abutment 9 directly beneath the piston crown. The locating portion-8 is-a-clos e fit in a corresponding bore 10 in the-crown endpart of thepi'ston l. I Opposite the junction of the 2 /2 inch and 2 inch diameter parts of the tubular piston rod, the internal diameter of the piston 1 is enlarged to about 4 inches so that in this region the piston has a thin skirt 11 (Fig. 4). This skirt is, however, thickened along two diametrically opposite sides by integrally formed longitudinal bosses which form semi-circular section ribs projecting from the interior surface of the piston skirt 11. The bosses are formed with axial screw-threaded bores to receive respectively two screw-threaded tension studs 12, 13 which both project about 1 inch below the lower edge of the piston skirt, i. e. about 1 inch to the right of said edge as seen in Figs. 1 and 2.

The tubular piston rod is bored transversely at 14 on a centre line just below the lower edge of the piston skirt, the bore having a diameter of nearly 1 inch and being adapted to receive a cross-pin 15 about 4% inches in length. The projecting ends of the cross-pin are bored on centre linesnormal to the centre lines of the cross-pin to allow free passage for the projecting ends of the tension studs 12, 13. Nuts 16, 17, which are fitted over said projecting ends on the side of the cross-pin 15 remote from the diesel piston 1, when tightened, pull the diesel piston firmly down on to the end of the piston rod 2, so that the said end is clamped tightly against the annular abutment 9 beneath the crown of the diesel piston. In order to achieve a compact assembly, the projecting ends of the cross-pin 15 are bevelled'as at 18, 19 on the side adjacent the piston 1 and correspondingly bevelled surfaces 18, 19 are formed on the adjacent ends of the semi-circular ribs of the piston skirt 11, the surfaces 18', 19 being separated from the surfaces 18, 19 by a small clearance.

The close fit of the locating portion 8 of the piston rod 2 in bore 10 in the crown part of the piston ensures good thermal contact between the latter and the piston rod.

As can be seen in Figs. 3 and 4, there is a relatively large clearance space 20 between the skirt 11 of the piston 1 and the opposite parts of-the piston rod 2, the mouth of.whichclearancespacejp isonlychstructed to a very small. extentby the, radially projecting end portions of the cross-pin 15. l

Theremovalofi thepistoml from the piston rod Z is more r, m t v ly imple. p t in n e. he nuts 16,, 17 have-been unscrewed from the projecting ends of the studs 12 13, itis a simplematter to withdraw the, locating portion 8 o f,the,pist0n rod from the bore 10 in the pist0n-crown.

I claim;

1. A detachableconnection between'a diesel piston and its piston rod in;a free-piston, internal-combustion operatedair-compressor, whereina substantial clearance is provided. between, the piston: rod; and the skirt of the diesel piston, which, clearance extends from the lower edge of theskirt towards, the crown, of the piston over a substantial distancc,,whilst, the extreme end portion of the piston, rod is a close coaxial fit within the diesel piston beyond, this clearance, said piston rod having a transverse bore, a cross pin fitted in said-bore and pro viding a pair of diametrically opposite radial projections located, adjacent the mouth of said clearance, and a pair of serewrthread tension studs interconnecting said radial projections. and the. open end of the, piston skirt for holdingthe piston rod againstthe crown of the diesel piston.

2. A detachable rigid connection between a diesel pistonand its ,piston rod in a,free-piston, internal-combustitan-operated air-compressor, wherein a substantial clearance is provided between, the piston rod and the skirt of the diesel piston, which clearance extends fromthe lower edge of the skirt towards the crown of the piston over a substantial distance, whilst the extreme'end portion of the piston rod is a close coaxial fit withinthe diesel piston beyond this clearance, said piston rod havingdiametrically opposite radial projections located adv 4. jacent the mouth of the said clearance and a screwthreaded tension stud" beingprovided-- interconnecting said piston skirt with each of said radial projections and holding said extreme end portion of said piston rod rigidly up against the crowmofthe diesel piston.

3. A detachableconnection as claimed in claim 2, wherein the radialfprojeetions carried by the piston rod do not obscure more than one quarter of the annular learance at hetmouth o isaid nnular space.

4; A detachable; cenne i nt s m in l m 2. wherein said radial projections .havetbevelled surfaces on the side facingtowards the piston skirt, and the lower edge of the piston skirt is formed with correspondingly bevelled, surfaces, the bevelled; surfaces on, the radial projections and those on. the lower edge of the piston skirt being separated by-a,srnall clearance when the detachable connection is secured.

5. A detachable connection as. claimed in claim, 2, wherein the piston skirt is.thickened along two diametrically opposite sides by integrally formed ribs projecting from theinterior surface of the piston skirt.

6. A detachable connection as claimed in claim 2, wherein facing surfaces of said radial projections and said piston skirt are sep arated by a small clearance when the detachable connection is secured.

References Cited in the file of this patent UNITED STATES PATENTS 839,446, Anderson Dec. 25, 1906 1,521,388 Pielstick Dec. 30, 1924 1,581,255 Watts Apr. 20, 1926 1,909,004 Parsons May 16, 1933 2,216,577 Stillwagon Oct. 1, 1940 2369,5001 Waeber Feb. 13, 1945 2,380,901 Hall July 31, 1945 OTHER REFERENCES Ser. No. 41,8,-6 64, Neugebauer (A. P. 0.), published 82 943- 

